Apparatus for heat treating porous sheet material



L. E. HUFFMAN 3,192,560

APPARATUS FOR HEAT TREATING POROUS SHEET MATERIAL July 6, 1965 4Sheets-Sheet 1 Filed Nov. 8, 1963 FIG.

INVENTOR LOWELL EVAN HUFFMAN ATTORNEY July 6, 1965 E. HUFFMAN 3,192,560

APPARATUS FOR HEAT TREATING POROUS SHEET MATERIAL Filed Nov. 8, 1963 4Sheets-Sheet 2 FIG.3

INVENTOR LOWELL EVAN HUFFMAN @we W ATTORNEY July 6, 1965 L. E. HUFFMAN3,192,560

APPARATUS FOR HEAT TREATING POROUS SHEET MATERIAL Filed NOV. 8, 1965 4Sheets-Sheet 5 .5 f8 24 /e -'I0 j as 39 5a 531 2? :32 a f 4 W a 4.6x

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y' INVENTOR LOWELL EVAN HUFFMAN ATTORNEY July 6, 1965 HUFFMAN 3,192,560

APPARATUS FOR HEAT TREATING POROUS SHEET MATERIAL Filed Nov. 8, 1963 A 4Sheets-Sheet 4 LOWELL EVAN HUFFMAN ATTORNEY United States Patent3,192,569 APPARATUS F012 HEAT PGRGUS SHEET MATERHAL Lowell Evanl-iufi'man, Wilmington, Del., assign-or to E. H. du iout de Nemours andCompany, Wilmington,

Dei, a corporation of Delaware Filed Nov. 8, 1963, Ser. No. 322,419 11Claims. (Cl. 13il) This invention relates to an apparatus for uniformheattrea-tment of porous sheet materials, in particular to an apparatusfor effecting such heat treatment while maintaining a restraint on thesurface of the sheet to prevent or minimize any change in areadimensions.

The heat treatment of porous sheet materials, for example nonwovenfabric webs or paper-like sheet structures, is often required in orderto activate a binder material therein, to modify the surface fordecorative or smoothing effects, to cause spontaneous elongation of theconstituent fibers thereby developing fiber crimp, or for other knownpurposes. In many instances the heat treatment requires the use of aclosely controlled temperature and rapid attainment of that temperaturein order to prevent adverse effects upon the resulting sheet material.

While nonwoven fabrics can be bonded by any of the well-known solvent,adhesive or heat bonding techniques, the latter in which the fibers areself-bonded at a multiplicity of fiber intersection points possessesdistinct advantages in terms of cost and the avoidance of the extrasteps which are otherwise needed to apply a binder material and remove avolatile carrier should one be used. Moreover, special effects can heoften achieved by selfbonding techniques which are not readilyattainable by other methods. A notable disadvantage of the self-bondingtechniques as heretofore practiced, however, has been the lackofequipment which, when employed in a continuous operation on a commercialscale, will provide the high degree of precision required with respectto tempcrature control. Thus if the temperature is not consistentlymaintained at a sufiiciently high level, areas of the fabric may possessan inadequate number of satisfactorily strong bonds. Excessively hightemperatures, on the other hand, give rise to over-bonding even to thepoint where the fiber structure collapses. In the case of orientedfibers such as crystalline oriented polypropylene, these being ofparticular value in nonwoven fabrics, the use of temperatures near theincipient melt point or stick temperature tends to deorient the fibersto such an extent that much of their inherent high strength isdestroyed. Even apart from the temperature control problem whichpreviously has been associated with self-bonding equipment, problemshave also been experienced in preventing excessive fiber shrinkageduring bonding. This problem has proven to be particularly acute withcrystalline polypropylene fibers since it has been observed that theytend to undergo excessive shrinkage even when bonded under carefullycontrolled conditions. iarticular care must therefore be exercised toensure that such fibers are properly restrained during the heatingoperation.

In processing a loose bulky web of nonwoven fibers, it is desirable toexpose all the fibers to a similar heat treatment so that the resultantproduct has a uniform distribution of equal bond points throughout itsdimensions. In practice, subjecting a Web of this kind to such criticalheat treatment by conventional means, gives rise to some exceedinglydificult and sophisticated heat transfer problems. This is largely dueto the high amount of dead air space contained in the web. The air isnot only a relatively poor heat transfer medium but, during actualtreatment, appears to absorb a large portion of thermal energy so thatgreat quantities of the heating medium must be supplied at a relativelyhigh temperature. Although high heat transfer rates may be establishedby introduction of the heating medium at a considerably highertemperature than the melt point of the fibers, in doing so, the fiberslocated near the surface of the web become overheated and frequentlydestroyed before the inner ones barely attain bonding conditions.Conversely, introduction of the heating medium at or near the melt pointresults in a correspondingly lower heat transfer rate requiring longerexposure of the web at the elevated temperature; from the standpoint ofeconomics, the additional time to achieve the proper degree of bondingis prohibitively long.

Moreover, in processing nonwov-en webs of polypropylene or other fiberssome means must be employed to restrain shrinkage in that portion of theweb undergoing treatment. The character of the restraint must not onlybe sufficiently low in magnitude so as not to crush the fibrousstructure but it must be applied very uniformly in a bi-directionalmanner across the web, otherwise nonuniform shrink-age of the fiberswill occur resulting in an inferior and unattractive product. Theproblem becomes increasingly troublesome as larger width webs areprocessed on a continuous basis; in which case, the ability to place auniform restraint on the web determines to a large extent whether theproduct is commercially saleable.

It is accordingly an object of the invention to provide an apparatus foruniform heat treatment of wide sheet materials under closely controlledtemperature conditions.

Another object of the invention is to provide an apparatus for heattreating a continuous web of material which is capable of supplyinglarge quantities of heat at a high rate Within a narrow, preciselycontrolled temperature range near the lower end of the melting pointrange of the material.

A further object of the invention is to provide an apparatus for heattreating a continuous web of material of very wide dimensions, underuniformly distributed restraining forces during the heat treatment.

A still further object of the invention is to provide an apparatus forheat treating a continuous web of material by uniformly heating the weband rapidly cooling it after treatment. a

The apparatus of the invention comprises a pressure vessel havingentrance and exit openings and containing first and second restrainingmeans each providing an endless conveying surface. The endless conveyingsurfaces are positioned adjacent opposite major surfaces of the sheetmaterial so that the sheet material is caused to pass, in sandwichfashion, into the entrance opening through the vessel and out the exitopening. The first restraining means comprises a substantiallyimperforate flexible band, such as a metal belt, which divides thevessel into two generally fluid tight chambers during its traveltherethrough. On one side of the imperforate belt is a first chamberthrough which the sheet material passes; on the other side is a secondfluid tight chamber. Each chamber is provided with a means forestablishing a fluid under pressure therein, i.e., so that the chambersare sep arately pressurized. The fluid in the first chamber is a heatedfluid, the fluid in the second chamber may be heated or unheated. Thesecond restraining means is perforate so that the heated fluid of thefirst chamber can flow therethrough and communicate with the sheetmaterial passing through the vessel and effect the desired treatment,e.g., bonding. Additionally this second restraining means also functionsas a support such that upon establishment of a hi her fluid pressure inthe second chamber than exists in the first chamber, the sandwich issecurely held together under restraining forces.

As will be apparent from the illustrated embodiments and the detaileddiscussion hereinafter, the invention is susceptible of numerousvariations. In one embodiment, for example, the second restraining meanswhich provides a support during imposition of the restrainin forces cancomprise a foraminous rotatable drum provided with a perforated endlessband. Alternatively it can comprise a foraminous platen, eitherstationary or not and having either a planar or curved surface, which isalso provided with a perforated endless band.

In a preferred embodiment of the invention, the apparatus utilizes thehigh heat capacity, excellent heat transfer and temperature uniformityof a saturated vapor atmosphere at superatmospheric pressure. While anysaturated vapor atmosphere which does not solvate or otherwise adverselyaffect one or more of the constituents of the sheet material may beused, saturated steam is the preferred medium because of favorableperformance, cost and availability factors. For convenience in theensuing discussion, reference will be frequently made to steam as theheated fluid but it will be understood that the remarks apply equally toother suitable vapor atmospheres.

By the creation of separate pressurized chambers, as described above,with establishment or" a pressure differential between the two, thesheet material passing through the vessel is firmly secured betweenendless surfaces moving at essentially the same speed as the sheetmaterial. As a result, pressure is uniformly applied to the sheet acrossits surface dimensions and any tendency for it to undergo a change inarea dimensions, e.g. shrinkage, is minimized. In terms of theuniformity with which the restraining forces are applied to the sheet,the utilization of a fluid pressure differential according to theinvention is quite superior to mechanical tensioning devices which mightappear to be satisfactory for accomplishing such an effect. This isparticularly true in the case of wide webs, for example of feet width ormore. The apparatus of the invention possesses still other advantages,however. Thus it permits a high degree of precision with respect totemperature control because the heated fluid supplied to the firstchamber quickly permeates the sheet so as to effect a uniform treatment,for example bonding, throughout the thickness dimension of the sheet.The apparatus is also of particular advantage when it is desired tosimultaneously produce a patterned surface upon the sheet being treated.

Being uniquely adapted to readily provide a closely controlledtemperature throughout the sheet being treated, the apparatus of theinvention is of particular advantage for still another reason. Thus whenutilized to create bonding sites between thermoplastic fibers in anonwoven Web, it permits rapid attainment of bonding temperatures whileminimizing losses in the fiber identity or changes in the molecularorientation of the fibers. By avoiding excessive changes in the fibers,tensile strength, tear strength, and other properties of the resultantsheet material are kept at a high level.

Because of the above-enumerated advantages, the apparatus of theinvention is particularly suitable for purposes of bonding nonwoven websof crystalline oriented polypropylene. With such webs an operating steampressure is normally selected in the range o1 about 38 to 131 p.s.i.g.corresponding to a temperature of about 14-0- 180 C., and this can bereadily maintained over continuous periods of operation. The apparatusof the invention is also well adapted to efiect self-bonding of nonwovensheets of film-fibril strand material, 6.". as described in Blades etal. US. Patent 3,081,519 issued March 19, 1963. Coherent, nonwovensheets formed by the multidirectional overlapping deposition of suchstrand material are described in Belgian Patent 625,998. The uniformtemperature and shrinkage restraining features of the apparatus of theinvention make it possible to self-bond film-fibril sheets and produce ahighly abrasion resistant surface on the sheet while maintaining a highlevel of opacity and uniformity of opacity.

,lsaseo The apparatus of this invention is further described byreference to the following drawings in which:

FIGURE 1 is a schematic representation of the operation of apparatuswhich utilizes a perforated drum.

FIGURE 2 is an elevational view of apparatus whose operation isschematically illustrated in FEGURE 1.

Pl-GURE 3 is a perspective view or" the apparatus of EEGURE 2, the coverhaving been removed and parts having been broken away and shown insection to reveal details of construction.

4 is a fragmentary cross section of the apparatus of FIGURE 3 viewedalong irregular line 1V' .TtV.

FIGURE 5 is a fragmentary cross section of the apparatus of FIGURE 3viewed along irregular line V-V.

Fl-GURE 6 is a schematic representation of the steam fiow feature of theapparatus of FIGURE 3.

FIGURE 7 is a fragmentary, cross section, elevational view of a planartype embodiment of the machine.

FIGURE 8 s a perspective view of the planar type apparatus of FZGURE 7,parts having been broken away and shown in section to reveal details ofconstruction.

As shown schematically in FIGURE 1 and in greater detail in FIGURE 2,the apparatus of this embodiment comprises a stationary frame havingupright supports 1 which are spaced apart and braced at the top by across brace 2 and secured at the bottom to a base 3, a pressure vessel 4fixedly secured between the supports 1 and equipped with inlets 15 and16 for supplying an atmosphere of fluid, e.g. pressurized saturatedsteam from any convenient steam generator source, not shown, into eachof the generally fluid tight chambers 23 and 24, respectively, arotatably mounted drum 5 housed in the vessel 4, pressure seals 6 and 7situated at entrance and exit openings, respectively, on either side ofthe vessel for passing a web id of sheet material therethrough, upperand lower endless conveying bands 5 and 9 which enter and leave vessel 4in a sandwiched manner through the respective pressure seals and whichpass around the drum 5 conveying therebetween the sheet material it tobe treated. The two bands, the sheet material, and the drum surface alltravel at essentially the same speed through vessel 4. Optionally anaddititonal pervious band, not shown, may be used to carry the sheetmaterial from a supply source or web laydown operation.

till referring to FIGURES 1 and 2, the upper band 8 is essentially animpervious endless belt of predetermined width. Being impervious, band 8cooperates along its lateral edges with the walls of vessel 4- toseparate that vessel into a first, in this case lower, generally fluidtight chamber 24 (which, of course, contains drum 5 and the length ofsheet material it) being treated) and into a second or upper generallyfluid tight chamber 23. he endless band 8 is constructed of a flexiblematerial so that upon creationof a higher pressure in chamber 23 than isprovided in chamber 24, it is uniformly pressed against the sheet 19which is supported by perforated band 9 and toraminous drum 5. In thisway the necessary restraining forces upon the sheet are provided. Band 8may be prepared from a thin gauge stainless steel sheet whose ends arebutt welded together and ground flush. Its external surface, that is,the side which lies in adjacent contacting relationship with the web Itmay be clothfaced or otherwise have an embossing pattern therein forimprinting a similar aesthetic pattern on the heattreated product andfor facilitating separation of the product after the treating operation.It should be noted that'the surface of imperforate band is notrestricted to a cloth-facing but may have any variety of characteristicslimited only by the desired end product. In addition, the band 8 may befabricated of a temperature-resistant elastomeric mate ial which issuitably reinforced by either a wire or fabric carcass. For example, awire screen belt embedded in an ethylene/propylene elastomer has beenshown to perform satisfactorily. The band 3 is suitably trained over asystem of rolls comprising an adjustable guide roll 11, idler rolls 12and 13, and a movable tension roll 14. Idler rolls l2 and 1.) arerotatably journaled at their ends in conventional bearin supports whichare fastened to suitable brackets on the supports l. -f desired, idlerroll 13 may be cooled by means, not shown, to increase the rate ofcooling of the sheet material as it leaves the pressure vessel. I

A commercial type sensor 13 mounted on arm 1) extending from the frame,engages the edge of the belt 8 and monitors its position relative to themachine frame during operation. Belt guide roll ill is provided withconventional adjusting means to shift and/ or tilt the roll slightly ineither direction along its rotational axis, thus forcing the belt totrack laterally. Any lateral deviation of the belt 8 is detected andtranslated into a signal which activates the roll-adjusting meansthereby causing the belt 3 to track laterally in a corrective direction.Once the belt 8 is adjusted and aligned with the entrance and exit seals6 and "I, the sensor 18 is intended to respond rapidly to relativelyminor deviations and initiate corrective action. Any gross laterialshifting could not only seriously damage the end seals and the belt, butcould create an open condition in the seals and thereby cause excessiveleakage of steam. The bands 8 and 9 as well as sheet material 16 arepreferably of only a slightly narrower width than the vessel entranceand exit openings.

Tension roll 1 is rotatably journalcd in a frame which is pivotallyconnected to the frame of the apparatus. Conventional means are employedto pivot the roll 14 outwardly thereby causing the band 3 to tighten.

The lower band 9 passes over a roll system which is functionallyidentical with the upper band 3 system, hence it is not described. Thelower band 9 is, however, perforated to permit the passage of heatedfluid from inlet 16, into the drum, and through the perforations 2.5 ofthe drum so that the fluid can contact the sheet material during itspassage through the vessel. Band 9 may be constructed of aheat-resistant material, eg. an elastorner which has been vulcanized toa fine wire screen. The principal purp se of perforations 17, shown indetail in FIGURES 4, 5, and 6, is to control steam distribution into thestructure of the sheet material during treatment in the vessel 4. Theseperforations 757 may be of circular, rectangular or other suitablegeometric cross section and are sized and spaced to facilitate steam distribution and sealing at the vessel entrance and erdt openings. In oneembodiment, for example, the holes may be circular and may range up to(3.38 in. diameter without deleterious effects on the surface qualitiesof the sheet material it). Perforations of 9.094 in. diameter are highlysatisfactory when provided in sufficient frequency such that the beltcomprises at least 5 open area.

As shown in FIGURE 1, the bands 3 and pass around the drum 5. Band 8divides the vessel into an upper chamber 23 and a lower chamber 24.Steam is supplied to the upper chamber 23 through an inlet 15 at aslightly higher pressure than in the lower chamber 24. The differentialpressure serves as the clamping means which exerts a uniformlydistributed force over the area of the band 8 communicating with thechamber 23, thereby pinning it against the relatively infiexi le surfaceof drur 5. The latter thus serves as a support for the bands and sheetduring passage through the vessel i. In this way the sheet material ltlsandwiched between the bands is firmly clamped across its majordimensions and thus shrinkage is effectively restrained.

In the preferred embodiment of this invention, a 2 p.=s.i.g.differential between the chambers provides stiflicien-t restraint on thesheet material it to avoid undue shrinkage during the heat treatment.Pressure differentials of up to 10 p.s.i.g. or more may be used ifdesired.

Drum 5 contains a plurality of openings 25 which connect the interior ofthe drum with the surface. These openings serve as passageways for thesteam to enter the interior of the drum from the lower portion ofchamber 24 and also serve as passageways by which the steam contacts thesheet material 10. It will be understood that a sufficient number of thedrum perforations 25 must coincide with perforations 17 of band 9 inorder to permit pass of steam into sheet material 1.9.

In the preferred embodiment, as shown in FIGURES 3 and 4, the curvedsurface of drum 5 is Wholly contained within chamber 24. As can be seenfrom these figures, the width of sheet it is slightly less than that ofbands 8 and 9. The bands are also wider than drum 5. Because of theflexibility of band 8 and owing to the greater pressure established inchamber 23, the two bands directly contact one another at the edges ofthe sandwich, indicated generally as area 2@, in fluid tight engagement.The abutting bands in area 20 overlap projection 42 of the side walls ofvessel 4. Projection 42 is a U-shaped stationary member that curvesaround about of the drum surface. A small clear ance Z1 is providedbetween the leading edge of projection 42 and the rim of drum 5. As thedrum 5 rotates with the sandwiched sheet being supported thereon, band 9slides along the upper surface of projection 42 to form a fluid tightpressure seal. The provision of a hardened metal surface portion 2-2aftlxed onto projection 42 assists in prolonging the life of theapparatus.

In alternative embodiment, not shown, the width of bands 8 and d can beless than that of the surface of drum 5. An adequate seal is obtained bycausing the smoothly machined rim of drum 5 to ride in rubbing contactwith the leading edge of projection 42, i.e. clearance 23 is virtuallyeliminated. if desired for this purpose, portion 22 may be spring loadedso as to be securely urged into contact with the rim of drum 5 tothereby accommodate any end-play and reduce wear.

With reference to FIGURES l, 2 and 3 a pulley, not shown, is attached toone end of the shaft on which the drum 5 rotates. This is coupled to anadjustable-speed electric motor or other power source to rotate the drumat the desired rate. The drum 5, in turn, serves as the driving meansfor recirculating the belts 3 and 9. Auxiliary motors or controlledtorque devices, not shown, synchronized with the drum-driving motor maybe used to drive rolls ll, l2, l3 and 34, thereby reducing the amount ofpower that must be transmitted by the drum to the bands. 7

In the embodiment of this invention described above, the entrance andexit seals 6 and 7 are structurally and functionally identical; hence,for the sake of simplifying the discussion, only one seal arrangementwill be described in detail.

In FIGURES 3 and 5, the exit seal 7 is shown in detail as comprisingthree stages of pressure-actuated members grouped serially along thelong, relatively constricted passageway 33 formed by an extension of thevessel 4 wall. Since all three stages are structurally identical, onlythe innermost stage is described in detail. The cffec'tive width of thepassageway 33 is slightly greater than the thickness of sheet lid andbands. interrupting the passageway '33, between the chamber 23 and theatmosphere, is a generally rectangular groove 34- which extends thewidth of the pressure vessel 4. Slidably housed in the groove 34 is amatching, generally rectangular-shaped shoe '36. The face of the shoe 36is recessed to accom modate a cylindrical roller 37. The shoe is urgedtoward the bands by a plurality of spaced compression springs that arehoused in groove 34. The shoe fits loosely in the groove 34 so thatsteam from chamber 23 may readi-ly flow along the top interface andpressurize the interior of the cavity 3%. As a result there is a,pressure drop from above to below roller 37. Most of the pinning forceexerted by the shoe 36 is derived from the steam pressure of chamber 23;a small fraction, however, is due to springs 38 which serve to augmentthe pinning effect of the steam. The magnitude of the total pinningforce regulates the extent of steam seepage through the fibrousstructure and determines the extent of compression of the sheet materialand also the amount the sheet material is preheated and cooled. Thislatter effect is described later.

Shoe is preferably constructed of some low-friction material, e.g.polytetrafiuoroethylene, to permit the roller 37 to rotate easily inContact with impervious band 3.

While the roller-seal is preferred for use on the impervious band 8, itis not quite so suitable for use on the opposite side of the bandsandwich, i.c. forated band 9, because of the problem of steam leakage.Although steam leakage can be minimized by selection of a suitabledesign and size for the perforations in band 9 and by use of largerrollers or a greater pinning force, it is preferred to utilize apressure-actuated shoe in direct contact with the perforated band 9. Asshown in FIGURE 5, the shoe 59 can be a generally rectangularshaped,elongated strip which is slidably housed in cavity 51 and spans theWidth of passageway 33. The shoe Si) is relatively loosely fitted incavity 51 so that steam from the chamber 24 may readily flow along thetop interface and pressurize the interior of cavity 51. Each shoe 5% maybe modified by open grooves 52 and 53 which run parallel the length ofthe member and serve as steam chambers during operation. All of thesegrooves are connected to the interior of the cavity 51 by means of anetwork of passages shown generally by the numeral 54. interposedbetween the backside of the shoe 5% and the bottom of the cavity 5'1 area plurality of compression springs These are spaced at regular intervalsand serve to supplement the earn pressure by furnishing a predeterminedminimum force on shoe particularly during the early phases of startupopera tions when steam pressure is low. As shown in FIGURE 3, grooves 45 may be provided in extension of the vessel wall 4 to serve as steamflow paths under band 9 adjacent to vessel openings 6 and 7.

Shoe 56 may be constructed from a suitable, noncorroding tool steel ofpreferably, from a low-friction material such aspolytetrafiuoroethylene. If desired, a pressure-activated shoe of thetype shown at St) in FIG- URE 5 may also be used in direct contact withimpervious band 3 in place of the roller-seal 36, 37.

The steam that leaks past the first-stage seal operates the second stagewhich is, therefore, at a lower pressure. Likewise, the third stage(outermost seal) operates on the steam that leaks past the second stage.In situations where the heating fluid may be other than steam and whosevapors may be a hazard to operating personnel, it is necessary toeliminate virtually all leakage to the atmosphere. This may be done bysimply adding more sealing stages. For most purposes three stagesprovide adequate sealing since the maintenance of a set pressurecondition is the prime requisite and a small loss of steam can normallybe tolerated.

Means for sealing the end gap at the base of U-shaped members 42 and theends of the pressure seals comprises a module containing three springactuated bars which abut against the edge of the band sandwich.Referring to FIGURE 3, the end-seal member is an elongated bar 60 ofrectangular cross section which is one of three that is slidably mountedin a block 61, which block in turn, is attached to the vessel 4 byconventional threaded fasteners. Bar 69 may be recessed, as shown inFIGURE 3, to receive the ends of rollers 37 which extend beyond the edgeof the band sandwich. The end face 62 of bar 60, which contacts the edgeof the bands, is a hardened, non-corrosive tool-steel alloy withlong-wear-life properties. The other end of bar 66 abuts against acompression spring 64 that urges the bar 69 against the bands. The otherend of the compression spring 64 abuts against a threaded sealing collar65 which slidably supports a slender push rod 66. One end of the rod 66is threadedly engaged to the bar 6% while the other end extendsexternally of the vessel l. This rod serves as a convenient means formanually retracting the bars fill in order to open the end gap and,thereby, purge any foreign material which may have become lodged thereinafter prolonged operation.

In the preferred embodiment, steam in the saturated condition is used asthe heating fluid to exploit the latent heat of condensation. Thepressure in the chamber 24 is adjusted to maintain the steam in asaturated condition near the melt point of the fibers, thereby making ita simple matter of controlling the bonding temperature very preciselywithin a narrow range. For example, in effecting self-bonding ofnonwoven polypropylene sheets, the steam may be maintained within i.l C.at a pressure of about p.s.i.g. Although steam is preferred, it shouldagain be noted that other condensable fluids can be used with equaleifectiveness.

Condensable fluids, as opposed to non-condcnsable fluids, offer aprecise degree of bonding because the fluid readily permeates thefibrous structures and rapidly reeases its latent heat at saturationtemperature which is identical to bonding temperature. Withnoncondensable fluids, a suitable temperature differential would berequired for rapid heat transfer. Since chambers 23 and 24- aremaintained separate of one another, the same fiuid need not be used ineach. Thus a noncondensable heated or unheated fluid such as air couldbe supplied to chamber 23 while steam or other heated condensable fluidis supplied to chamber 2- As shown in FIGURE 6, chamber 24 is situatedso as to promote gravity drainage of condensate within that chamber.Arrows marked S indicate steam entering the web it As best shown in FIG-URE 1, any excess condensate collects at the bottom of chamber below thedrum 5 and is later removed from there by some suitable means (notshown).

FIGURE 3 has, of course, been illustrated showing only the generallycircular end plates and seal containing portions of vessel In use athick metal covering is secured over the drum 5 and bands 3 and 9. Lugsin the covering may be inserted thru holes 43 in the end plates andsecured by nuts. Suitable conduits in the covering provide an inlet forsteam into chamber 23.

In operation, the sheet material it may be fed directly into the nipbetween bands 8 and 9 or may be transported on a pervious band from someupstream web laydown equipment or from a supply reel and fed into thenip of the bands 8 and 9; at which point, the web 10 is sandwichedtherebetween and carried in this manner into the pressurized vessel 4.As the web lit is transported into the chamber 24-, it passes throughthe pressure seal 6 whereupon the sandwich arrangement is subjected tolight pinning pressure. T he seal allows only a negligible amount ofsteam to leak past along the interfaces of the bands; however, a laminarflow of steam passes through the fibrous structure of the sheet material10 as shown by the arrows in FIGURE 6. This purges the air from thefiber interstices and heats the sheet material at an even rate as itenters the chamber.

Inside chamber 24 of the vessel 4-, the sheet material becomes permeatedwith the saturated steam supplied to that chamber and is rapidly heatedto bonding conditions. As the sheet material is transported through thevessel 4 between bands 3 and 9, the slight differential pressure betweenthe chambers acts upon the upper band 8 causing it to exert a uniformcontact pressure against the supporting surface of drum 5. This actionpins the interposed sheet material and effectively restrains the fibersfrom excessive shrinkage during passage through the vessel. Uponentering the pressure seal 7 at the exit end, the fibers are coveredwith moisture and are in a heat-softened state which precludes handlingwithout permanently damaging the fibrous structure. However, as thesheet material passes through the seal 7 to the atmosphere, the suddendecrease in pressure causes the moisture on the fibers to flash intosteam which exits through the perforated band 9 thereby tends to rapidlycool the web 10. As a result, additional downstream cooling and dryingapparatus are not required and the finished sheet material can behandled almost immediately.

As will be apparent from the drawings, particularly FIGURE 1, the sheetmaterial to be heat treated is maintained in a restrained condition,i.e. between the bands 8 and 9, a short time before it enters and afterit leaves the pressure vessel. The latter is of special significancebecause it ensures that the material has cooled sufficiently to avoidany shrinkage after the restraint is removed. Only a very brief periodof restraint outside the pressure vessel is required because thecondensed vapor on the sheet material, being at a temperature above theatmospheric boiling point, rapidly vaporizes and exits through theperforated band, thus removing heat from the sheet material when thepressure is reduced to atmospheric. For most efficient utilization ofthis efiect, it is desirable that the perforated band be in directcontact with the atmosphere after it passes through the exit opening ofthe pressure vessel.

Where process conditions involving low steam pressure and very lightuniform contact pressures are dictated, it may be desirable to isolatecompletely any clamping effects on the web arising from belt tensions.Accordingly, in FIGURES 7 and 8, an alternate embodiment of theinvention is shown which fulfills these requirements. In these figures,similar reference numerals designate similar parts referred to inFIGURES 1 through 6. The embodiment is different from that shown in FIG-URE 2, in that a planar support is employed in place of a rotating drumon which the belt sandwich rests in the treatment zone. The support maybe in the form of a series of closely spaced parallel rollers or aperforated moving conveyor but preferably is an inflexible stationaryforaminous platen 7 t Framework 69, suitably attached to walls of vessel4:, supports the platen 7% so that surface 77 and belt 8 form a boundarybetween upper chamber 23 and lower chamber 24. The platen 75B is thus ofa fixed location over which the belt sandwich is adapted to be advancedthrough the vessel 4. Means for recirculating the belts 8 and 9 areprovided by rolls 71 and 72, which are coupled to an adjustable-speedelectric motor (not shown). Belt tensioning and tracking are effected bytension rolls 73 and '74 and guide rolls 75 and 76, all of which areequipped with conventional means for adjustment.

As best shown in FIGURE 8, surface 77 is modified by an array of opengrooves 78 and apertures 7h that convey steam from chamber 24 to thebelt sandwich in a uniformly distributed manner. Although the groovearrangement sh wn extends generally parallel with the direction of belttravel, it will be apparent that any oblique angular relationship orcurvilinear pattern may be established. Alternatively, steam may bedistributed through a pattern of circular apertures or through astructure composed of a porous sintered material. The remaining portionof the surface 77, in rubbing contact with the belt 9, is treated toreduce the clamping efiect of the steam pressure which is converted intofrictional and high tensile forces in the belts. This may beaccomplished in a number of ways such as texturing the surface by eithermechanical brushing or chemical etching or preferably by an applicationof a thin layer of suitable material having a low coefiicient offriction as, for instance, chrome plate. The surface may also belaminated with certain organic compositions capable of withstandingelevated temperatures and having self-lubricating properties, forexample, polytetrafiuoroethylene.

In alternate processes, the apparatus is capable of manufacturing avariety of products having special eifects. For example, a dense highlycompressed, parchment-like material may be produced'by increasing thedifferential 19 clamping pressure between the chambers 23 and Z4 and thenet pinning force in the pressure seals 6 and 7. A product having asmooth, glazed finish may be readily achieved by processing a sheetmaterial in contact with a smooth-surfaced band. A composite structuremay be made such as fibers bonded to a film base wherein the film has ahigher melting temperature than the fibrous component. A composite of anonwoven sheet and film can also be prepared concurrently whileeffecting selfbondlng of the nonwoven sheet. For example, an unbondednonwoven sheet of oriented polypropylene filaments is placed next to theadhesive-coated side of a biaxially oriented polypropylene film.Branched polyethylene is a suitable thermoplastic adhesive. The layeredstructure'is then passed through the apparatus to effect simultaneousself-bonding of the nonwoven sheet and activation of the adhesivecoating on the film. The layered structure can be passed through theapparatus with either the nonwoven Web or the film being in contact withthe perforated band. In the former case, the steam permeates thenonwoven sheet structure as is the usual operating procedure for theapparatus. In the latter case, the steam contacts only the film since itis impervious and the entire steam pressure urges the film against thefibers. This effectively drives out the entrained air in the structure.When operating in this manner, it is possible to impart a glazed surfaceto the nonwoven web side of the composite by having it in contact withan impervious band having a smooth surface.

Since many different embodiments of the invention may be made withoutdeparting from the spirit and scope thereof, it is to be understood thatthe invention is not limited except to the extent defined in thefollowing claims.

What is claimed is:

1. Apparatus for heat treating a continuous length of sheet materialcomprising structure defining a pressure vessel having entrance and exitopenings, first and second restraining means each providing an endlessconveying surface for engaging, respectively, a major surface of saidsheet material and effecting passage thereof in sandwich fashion intosaid entrance openingthrough said vessel and out said exit opening, saidfirst restraining means comprising a substantially imperforate flexibleband which divides said vessel into a first generally fluid tightchamber through which the sheet material passes and a second fluid tightchamber oppositely disposed of the first, means for establishing aheated fluid under pressure in said first chamber and means forestablishing in said second chamber a fluid under a greater pressurethan in said first chamber, said second restraining means providing asupport for said sheet material and said imperforate flexible bandwithin said vessel whereby the pressure differential between saidchambers imparts restrain ing forces to the sheet material passingthrough said vessel, said second restraining means further beingperforate whereby the heated fluid of said first chamber communicateswith said sheet material in said vessel.

2. Apparatus of claim 1 wherein said second restraining means comprisesa generally inflexible perforate body portion supporting an endlessflexible perforate band which engages said sheet material within saidvessel.

3. Apparatus of claim 2 wherein said generally inflexible perforate bodyportion comprises a rotatable drum.

4. Apparatus of claim 2 wherein said generally inflexible perforate bodyportion comprises a stationary platen.

5. Apparatus for heat treating continuous lengths of sheet materialcomprising wall means defining a pressure vessel having entrance andexit openings, Within said vessel 21 supporting means having a generallyinflexible foraminous surface, first and second endless flexible bandstrained to run into said entrance opening upon the surface of saidsupporting means and out said exit opening, means for feeding said sheetmaterial to be treated between said bands, said first endless band beingsubstantially imperforate and cooperating with said wall means toseparate said vessel into a first generally fluid tight chambercontaining said supporting means and through which the sheet materialpasses and into a second fluid tight chamber oppositely disposed of thefirst, and means for establishing a heated fiuid under pressure in saidfirst chamber and means for establishing a fluid under pressure in saidsecond chamber, said second endless fiexible band further beingperforated whereby the heated liuid of said first chamber communicateswith said sheet material.

6. Apparatus of claim 5 wherein the face of said first endless flexibleband which is in contact with said sheet material has an embossingpattern therein.

7. Apparatus of claim 5 wherein the face of said first endless flexibleband comprises a smooth surface sheet.

8. Apparatus of claim 5 wherein the face of said sup porting meanscomprises a rotatably mounted drum.

9. Apparatus of claim 5 wherein the face of said supporting meanscomprises a stationary platen.

19. Apparatus for heat treating continuous lengths of sheet materialcomprising structure defining a pressure vessel having entrance and exitopenings, first and second endless flexible bands for engaging saidsheet material therebetween and effecting passage of said sheetmaterialin sandwich fashion into said entrance opening through ber a fluid undera greater pressure than in said first chamsaid vessel and out said exitopening, said first endless band being substantially imperforate and,separating said her, and a rotatable drum positioned within said firstchamber and supporting the sandwich of said bands and sheet materialduring the major portion of its passage through said vessel, the surfaceof said drum and said second band being perforated whereby heated fluidin said first chamber can fiow into contact with said sheet material.

il. Apparatus for heat treating continuous lengths of sheet materialcomprising structure defining a pressure vessel having entrance and exitopenings, first and second endless flexi le bands for engaging saidsheet material therebetween and effecting passage of said sheet materialin sandwich fashion into said entrance opening through said vessel andout said exit opening, said first endless band being substantiallyimperforate and separating said vessel into a first generally fluidtight chamber having the sheet material disposed therein and a secondfiuid tight chamber oppositely disposed of the first, means forestablishing a heated fluid under pressure in said first chamber andmeans for establishing in said second chamber a fluid under a greaterpressure than in said first chamber, and a stationary platen positionedwithin said first chamber and supporting the sandwich of said bands andsheet material during the major portion of its passage through saidvessel, the surface of said platen and said second band being perforatedwhereby heated fluid in said first chamber can flow into contact Withsaid sheet material.

References Cited by the Examiner UNITED STATES PATENTS 2,543,101 2/51Francis 156-376 XR 3,088,859 5/63 Smith 156-369 3,098,260 7/63 Richessonl8-6 WlLLIAh i J. STEPHENSON, Primary Examiner.

1. APPARATUS FOR HEAT TREATING A CONTINUOUS LENGTH OF SHEET MATERIALCOMPRISING STRUCTURE DEFINING A PRESSURE VESSEL HAVING ENTRANCE AND EXITOPENING, FIRST AND SECOND RESTRAINING MEANS EACH PROVIDING AN ENDLESSCONVEYING SURFACE FOR ENGAGING RESPECTIVELY, A MAJOR SURFACE OF SAIDSHEET MATERIAL AND EFFECTING PASSAGE THEREOF IN SANDWICH FASHION INTOSAID ENTRANCE OPENING THROUGH SAID VESSEL AND OUT SAID EXIT OPENING,SAID FIRST RESTRAINING MEANS COMPRISING A SUBSTANTIALLY IMPERFORATEFLEXIBLE BAND WHICH DIVIDES SAID VESSEL INTO A FIRST GENERALLY FLUIDTIGHT CHAMBER THROUGH WHICH THE SHEET MATERIAL PASSES AND A SECOND FLUIDTIGHT CHAMBER OPPOSITELY DISPOSED OF THE FIRST, MEANS FOR ESTABLISHING AHEATED FLUID UNDER PRESSURE IN SAID FIRST CHAMBER AND MEANS FORESTABLISHING IN SAID SECOND CHAMBER A FLUID UNDER A GREATER PRESSURETHAN IN SAID FIRST CHAMBER, SAID SECOND RESTRAINING MEANS PROVIDING ASUPPORT FOR SAID SHEET MATERIAL AND SAID IMPERFORATE FLEXIBLE BANDWITHIN SAID VESSEL WHEREBY THE PRESSURE DIFFERENTIAL BETWEEN SAIDCHAMBERS IMPARTS RESTRAINING FORCES TO THE SHEET MATERIAL PASSINGTHROUGH SAID VESSEL, SAID SECOND RESTRAINING MEANS FURTHER BEINGPERFORATE WHEREBY THE HEATED FLUID OF SAID FIRST CHAMBER COMMUNICATESWITH SAID SHEET MATERIAL IN SAID VESSEL.